Two-fluid refrigeration system



May 18, 1954 L. F. WHITNEY TWO-FLUID REFRIGERATION SYSTEM 6 Sheets-Sheet l Filed Oct. 4. 1949 f fwvemor L. F. WHITNEY May 18, A1954 2,678,548 Two-FLUID REFRIGERATION SYSTEM 6 Sheets-Sheet 2 Filed Oct. 4. 1.949

Mms-Zier May I18, 1954 L. F. wH|TNEY Two-FLUID REFRIGERATION SYSTEM s sheetssheat' 3 Filed oct. 4, 1949 i May 18, 1954 L F. WHITNEY Two-.FLUID REFRIGERATION sys'rm 6 Sheets-Sheet 4 Filed ot. 4. 1949 sun-huir- May 18, 1954 l. F. WHITNEY TWO-FLUID REFRIGERATION Filed Oct. 4. 1949 May 18, 1954 L F. WHITNEY 2,678,548

'rma-FLUID REFRIGERATION SYSTEM Filed oct. 4; 1949 e sheets-sheet e Ui 29 J9 J9 66 7j .74

Patented May 18, 1954 UNITED STATES PATENT OFFICE TWO-FLUID REFRIGERATION SYSTEM Lyman F.;Whitney, Boston, Mass., assigner, by `mesnc assignments, to Stator Company, a corporation of Massachusetts Application October 4, 1949, Serial N o. 119,489

(Cl. (i2-426) `9 Claims. l

This invention. relates to `refrigeration apra-iratus of the type shown in United States Patents Nos. 1,761,551 and 2,180,447, and moreparticularly` to an improved evaporator for such systems.

Conventional reirigerating apparatus embodies an evaporator disposed in heat transfer relation to thevcooling and/or freezing compartment and which contains a refrigerant, the vapors of which yarepuznped from the evaporator, condensed. .and the condensate then returned to the evaporator. Non-aqueous refrigerante having high vapor pressures evaporatetfreely throughout the `liquid mass by boiling, agitating the liquid mass and bringing it :ln-contact with vapor. Thus any por tion of the liquid mass located so asto receive heat from the Space to v.be refrigerated `can absorb that heat `continuously by ebullition. The same is not true of aqueous and other refrigerants having low volatility, for at thelovv` temperatures required by present-day 4refrigeration their Vapor pressures are 'so low that in the absence of dissolved gases no bubbles will ordinarily form below the free surface of` the liquid `unless the latter `becomes substantially superheated. Thus the mass is not agitated by boiling, and the free surface ,get-s all the cooling, which is not readily communicated elsewhere due to the low` heattransmissivity of `quiescent liquids. Hence, the coldest portion of the evaporator is that adjacent to the line of contact between liquid and vapor; which aiords `a limited areafor cooling an adequate refrigeration space. Enough copper, aluminum or other good heat-conductor to distribute the cooling effect Would be bulky.. expensive .and generally impractical.

`Although the trouble could theoretically be remedied by introducingthe condensed refrigerant at a point close to the top of the evaporator so as to trickle down the evaporator ,walls Ain a thin film, as a practicalmatter this method encounters certain diiliculties including a need' for precise levelling to spread the .flow to .all sides oi' the evaporator. Relatively slight mislevelling .tends to llood `one portion of the Walls and leave the rest dry.

The diiiculty is aggravated by the need of a dissolved volatile antifreeze. .An ideal `substance 'for this purpose would Vaporize with the .water in unchanged proportions .(azeotropic solution), Abut such solutions .are not very common at any spec ilicd temperature and pressure, `and the anti ireeze must 'meet so many other requirements (such as thermal stability; `non-reactivity with water. :i1-onor mercury; non-emulsifying tendamy, ete.) :that only a rough `appranimation.to the vdesired volatility has yet been achieved. `Too volatile a substance would cause prohibitive `difficulty by failure to condense fully with the water vapor, blocking the condenser with accumulated vapor and causing the pressure to rise too high for the ejector to pump against it. This leaves, as the `lesser evil, a choice of antifreeze which vaporizes less readily than the water and accumulates at the evaporating sur-face, lowering the vapor pressure.

The principal objects of the present invention are` to overcome the aforementioned difficulties and to provide a system eiective to insure adequote evaporation of refrigerant with littlesuperheating, and to distribute the .cooling effect throughout an extensive refrigeration space and control its temperature, Without requiring rela-` tively costly, heavy or bulky apparatus.

A more specific object is to provide an efficient heat conveyor to absorb heat from a substantial frozen food space .and deliver it at a higher gravitational level to the restricted region Where the aqueous refrigerant can `absorb said heat by evapora-tion.

A further object is to provide an improved purging system which is designed so as to insure continuous removal of extraneous gases from the system without danger of becoming sludge-bound- Further objects reiate to various features of construction and zvill be apparent from a consideration Vor the iollowing disclosure.

i accordance with .the `present invention I provide :a refrigerating apparatus or system which includes a compartment having therein an enclosed evaporator or cooler containing a normally .liquid primary refrigerant, such .as water containing a suitable antifreeze agent, spaced below the upper wall of the evaporator, so as to provide a liquid-vapor interface. Disposed within the evaporator is a portion of an enclosure adjacent to the vliquid-vapor interface .so as to transfer heat thereto, and another :portion of the enclosure is disposed outside the evaporator and at a level helow the 1iquid-vapor interface but in heat trans fer relation to the storage compartment :so as to receive heat therefrom. This enclosure conta-ins a duid .or `secondary refrigerant having a vapor pressure greater than water or the primary refrigerant in the evaporator and is normallt7 under such pressure as will cause it to circulate .thro-ugh the enclosure in response to a temperature dif ferential between the liquidyapor interface and the interior of the compartment byreasonof the secondary uuid `receiving heat `from the storage compartiment which results Yin .vaponization the or refrigerant may be in the form of a housing l in telescoping relation to the evaporator and in heat-transfer relation to the main compartment; or it may be in the form of acoil, a conduit or other enclosure having a part in heattransf er relation to the liquid-vapor interface and another part in heat-transfer relation to the main com.-I

partment and at a level below the liquid-vapor interface, as shown in the accompanying draw ings which illustrate different embodiments of the invention as applied to a modern domestic refrigerator.

u In the drawings: Fig. 1 is a diagrammatic View of a complete. refrigeration system embodying the present in. vention;

Fig. 2l is an enlarged top plan view, wlthY parts broken away, of the evaporator or cooler shown in Fig. 1;

Fig. 3 is a front elevation of the cooler shown in Fig. 2;

Fig. 4 is a section on the line 4-4 of Fig. 3; Fig. 5 is a diagrammatic view of a complete refrigeration system embodying the modified cooler shown in Figs. 6-8;

' Fig. 6 is a front elevation of the modied cool- Fig. 7 is a section on the line l-l of Fig. 6;

Fig. 8 is a fragmentary top plan view of the.

cooler shown in Fig. 6;

Fig. 9 is a plan view of another modified form of cooler;

Fig. 10 is a section on the line Ill-I0 of Fig. 9;

Fig. 11 is a section on the line II--II `of Fig. 10; Fig.. 12 is and Figs. 13 and 14 are fragmentary elevations illus-l trating modified purger connections.

Referring to Fig. 1, the refrigerating system shown therein comprises a boiler I having a suitable heater such as a gas burner assembly 2 and a draft-inducing nue 3, only a portion of which is shown. Mercury vapor passes from the boiler I through a riser 5 to the branches 5EL and 5b which are connected, respectively, to the interconnected first and second stage aspirators 3a and 6b of a" multiple stage ejector. The first stage aspirator 5a is connected by a vapor duct 8 to my improved cooler.. or evaporator II (hereinafter more fully described) which contains a body of aqueous refrigerant containing a suitable antifreeze agent. Vapor is drawn through the duct 8 to the mixing chamber of the rst stage aspirator and the mixed propellant mercury vapor and the refrigerant vapors are passed through the aspirator where the refrigerant is compressed and the mercury is condensed. 'V'Ihe condensed mercury iiows from the rst stage aspirator into a drain I4 while the com,- pressed vapor passes through a duct I5 to the second stage aspirator 6b into which a second stream of mercury vapor ows from the line 55, this latter propellant stream causing a further compression of the refrigerant vapor in the secan elevation of my improved purger;

ond stage aspirator. Drains 21 and 21a receive the condensed mercury from the second stage aspirator and the two drains 2'I and 2IEL join the drain I4 at 28 and 28a, respectively, the drain I4 being connected to an inclined drain line 3| which is normally lled with mercury. The compressed refrigerant passes upwardly from the second stage aspirator through duct 29 to the refrigerant condenser 30. The condenser 30 may be of any suitable form and is here shown as Ibeing disposed within a water tank or reservoir T, as in Patent No. 2,174,302, granted September 25, 1939, to which reference may be had for a more detailed description of the system.

A chamber or drum 32 is preferably located at the end of the condenser 3B remote from the n inlet of the pipe 29, and one end of a pipe 39 communicates with the chamber 32 so as to receive noncondensable gases therefrom. The lower portion of this chamber is connected with a drain or refrigerant return pipe 34 through which the condensed refrigerant passes on its way back to the cooler II. Y

The lower end of return pipe 34 is connected. with the upper end ofthe inclined drain line 3| and also with a vertically extending double bend,

' having legs 43 and 4I through which condensed refrigerant standing in line 34 pushes throughv the mercury at its junction with leg 4|] and pipe 3d, and thus makes its way back to the cooler II. The junction 43 of the lower end of the drains 3l and I4 is connected with an upwardly inclined spill-over line 42 which is connected with the line 33 at 63, which connection determines the I normal mercury level L of the system.

The lower end ofthe leg 4I is connected to- 4 the intermediate portion of a vertical capillary and 45 provide a vapor lift, as' more fully ex-l tube 45, the upper and lower ends of which are respectively connected with inlet and outlet open ings at the top and bottom of the cooler II, as hereinafter more fully explained. The parts 4I plained in the copending application of Eastmany A. Weaver, Serial No. 60,881, filed November 19, 1948.

The lower end of coolerrII is provided withY a sludge drain 46 connected to the central part of a drum 48, the upper end of which is connected by a line 5I! with a mercury return pipe'and boiler' feed 52, and thelower end ofthe drum is con nectedby a line 5iuwith the return line 52 at aA level slightly higher than the junction of drain: 4B and drum 48. The upper end of this return line 52 is hooked so as to connect in at the top of vapor duct 8, and its lower end is connectedv to the inlet of boiler I. With this construction and arrangement of parts, mercury and mercury sludge (an emulsion of mercury in the aqueous refrigerant) accumulating in the lower part of the cooler I I now through drain 43 into drum 43 where they are subjected to the yaction of the',` low pressure in duct 8. Hence the emulsion or sludge is broken up by evaporation of the aqueousv component and the mercury is returned to the boiler, through line 52. I

As above noted,and as shown more clearly in Fig. 12, the spill-over line 42 and lower end of line 3,9 are connected at 60 so as to provide aY purger comprising a mercury pump ,in which drops or slugs of mercury run down a 'capillaryv tube 62, trapping noncondensable gases drawn,v from chamber 32 and compressing them to morethan atmospheric pressure. The lower end of tube 62 is connected with an inclined fitting or' pipe line 64, the upper end of which is provided with e vent cap tt open to' the atmosphere and the lower end ofwhicn isconnected to a return branch v88 `which in turn is connected with the return line l2. With this construction and arrangement the partsel, -64 and 68 provide a trap for the mercury which permits the entrapped gases carried down and compressed by the mercury to risel in the line 6l and escape through vent capte, while thefmercury returns through lines 68 and 62 to the boiler l. i i

The parts 62, 64, etc. are disposed in relatively close proximity to the riser and are enclosed by suitable insulating material within the conflnes'cf brokenline A `(Fig. l) so that they are normally maintained at a temperature above 212' F.. therebyfpreventing an accumulationof mercury sludge in any part of the 'purger sys tem.

Both the aspiratcrs 6 and 8 `are provided with cooling jackets interconnected by the duct "l0, the first stage aspirator i5a having a `cooling line or riser '1| `connected with a condenser l2 within the tank T which has the 4usual pumpeout connectioni, cold water supply line 8%, and hot water discharge line 61, asin Patent No. 2,174,302. The-water in `tank T is thus heated by the condensation of thefprimary refrigerant and the cooling fluid which absorbs a major portion of the heat of condensation from the mercury vapors.

Referring to Figs. 2 to 4, the cooler oomprises a hollow inner housing |0| and a hollow outer housing |02, the inner housing 40| having abottom wall consisting of a fiat inner plate |04 (Fig. 4) and a` corrugated outer plate |85. The plates |04 and |05 extend upwardly to form the inner and outer side walls |06 and |01 of thehousing ||l| (Fig. 3), and their top and end edge portions are sealed together so that the plates |114 and |05 `define an enclosure which receives a secondary :duid such as F'reon,` it being noted that passages in both the bottom and side walls deiined by vthe ccrmgations or reinforcing grooves intercommunicate with one another.

The housing 102 is generally similar to the housing |04 in that it comprises inner andouter plates H0' and ||1| formed with reinforcing dimples H2 which maintain them 4in properly spaced relation. These plates are shaped to provide a hollow, roofelilretop` wall llxand hollow depending'walls ||6 and |11 intercommunicating with each other. The enclosure orouter housing thus delined by the inner and outer `walls l l!) and ill receives the primary aqueous refrigerant which Vis normally at a level below the vapor` duct outlet Morand above the junction of tube 45 `with arm 4| so as to' provide at all times a liquidvapor l interface. The construction' and arrangement of parts are such that the outer 'side wall of the inner housing IBI is indirect heat transfer relationV tothe inner side walls of the outer heuslng so that vapors of .the secondary uid `in the upper `pari', :of the side walls ofthe innerhousing quickly transfer their latent .heat to that `portion of the inner side walls of the outer housing contiguous or ad-acont to the liquid-vapor interface which, of course, .has `a relatively lgreat heat-ab sorbing capacity. Thus, vapors "of the secondary fluid vtransfer' their latent heat `to the primary refrigerant which is constantly Vbeing `vaporized and ultimately the latent heat of therlatter is transferred to the water in tank T along withthe heat transferred `from the .fluid in the ycooling jackets.

\ The teleseoping housings `HN andwlz provide a storage compartment for receiving foods or articles to be stored, and the front may be pro vided with the usual doors (not shown) through which access to the .interior may be had. I use a vapor lift in this embodiment similar to `that disclosed in the copending application of Eastman A. Weaver serial No. 66,881, led November 19, 1948. To this end the inner plate H0 of the housing vIlll` is formed with a central trough |20, the bottom wall of which inclinesfrom rear to front, as shown in Fig. 4. The outer plate or wall is formed with an inlet opening madjacent to the rear of the trough and the upper or delivery end of capillary tube 45 communicates with the opening so as to deliver liquid refrigerant to the trough. The lower end of tube 45 is com nected to the rear bottom wall of the outer housing adjacent to its connection with the sludge drain 46.

The lower end of the trough |20 is connected with a J-tube |25 which provides a mercury trap operative 'to hold back the aqueous refrigerant in the trough and at the same 4time permit stray` particles or mercury to pass therethrough to the bottom of the outer housing and then into the' The wetted sloping top surface ofi drain 45. wall H0 is preferably roughened as `by vsand-- blasting or otherwise formed with capillary rugosities effective to distribute refrigerant overflowing from trough |29 over the maximum area,

as in my copending application Serial No. 36i932.'

In operation the vapor lift carries` refrigerant from both the lower part of the outer housing and the return line 3'4 to the trough |20 where it overflows onto the rugose surface of the wall i I0 and trickles down the `inner side walls where appreciable vaporization takes place. Since the inner side walls of the outer housing are in heattransfer relationto the outer side wall of the inner housing, the latent heat of the `secondary refrigerant is readily transferred to the primary refrigerant and hence the overall efiiciency and capacity of the system` is greatly increased.

The same basic principlesare illustrated in the embodiment of Figs. 5 to 8. The general system,

as shown in Fig. 5, is substantially the vsame as that shown in Fig. l, the same orzsimilar referencecharacters being applied to the same or` corresponding parts, but in place of a single tank T there is provided a pair of tanks T-I and T-Z interconnected by a pipe line and providedwith condenser jackets 8| and 32, respectively.` The jacket 8| is connected with the compressed refrigerant vapor line 29EL and provides a refrigerant condenser, and the jacket 8,2 is con nected with the cooling iluid line Ha and provides a condenser for the cooling fluid. The purger line 39 is connected to the chamber 32a at the end of jacket 8| remote from line 29a, and the valve for use in initially exhausting the system `is connected to the chamber 32a.

In place of the vapor lift shown in Fig. 1, I"

standing in line A31| pushes through the mercury at the junction with leg 40 to work its way back to evaporator or cooler 1| le. The lower enduof drain 4% is connected to sludge drum 48, the upper end of which is connected by aline 49 to vapor duct 8 and the lower end is connected by a line 5U both to the mercury return `52 and the vent e9,

the construction and arrangement of parts beingl such that sludge in the drum #is is subjected to the actionof the low pressure in duct t soV as to evaporate the aqueous component and permit the particlesof mercury to coalesce and eventually work back through line 50 to the return 52.

The cooler 11B (Figs. 6 to,8) is, in principle, similar to the cooler 11 and vcomprises a storage compartment C having an inner bottom wall 205 (Fig. .7) and a corrugated or grooved outer wall 202fjuxtaposed to the innerwall 201, both walls extending vertically so as to provide the side Walls of the compartment. The corrugations provide fluid passages 204 which are interconnected at the corners of the compartment by enlargements 205. The lower front edge of the outer wall 201 pivotally supports a pair of upwardly swinging closure members or doors 20e and the side walls of the compartment are provided with brackets 20B for anchoring the compartment in position.

The upper portions of the side walls are connected. with elongate headers 210, the bottom walls of which incline from rear to front and the rear or enlarged parts of these headers are connected with fa plurality of horizontally extending, closely spaced, flattened steel tubes 212. The passages 204, headers'210 and tubes 212 thus provide a continuous circuitl or enclosure which contains a secondary fluid or refrigerant such as Freon.

Extending substantially the length of the conipartment and surrounding the tubes 2i2 is the main evaporator or enclosure which is formed vof two similar sections 215 and 2 16, each consisting of a generally frusto-conical shell having a :Gange 218 at its enlarged inner end by means of which vthe two sections are joined, as shown in Fig. 6. The lower part of the junction of the coupling anges 218 is provided with an opening 220 which receives the duct 46 and the upper part of the section 21d is provided with a vapor outlet 222 to which the vapor duct 82 is connected, the construction and arrangement of parts being such that the lower portions of the tubes 212 are at all times immersed in the liduid refrigerant, the normal level of which is just above the lower portions of the tubes 212. The' opening 222 must not of course extend below theY desired liquid le'vel which is maintained by a .part of the wall of section 216 extending up within the welded end of vapor-duct 8a to form a lip' 223 (Fig. 7), turned slightly inward to keep spray from passing into the vapor-duct a. The exterior of the tubes 212 maybe sandblasted or otherwise provided with capillary rugosities so that liquid refrigerant creeps over the exposed surfaces of the tubes and keeps them wet with a' by brackets 226, provides the lower part of theA rear wall.

It Awill be noted from the foregoing that th sections 2 i 5 and 215 constitute an enclosed evaporator containing the primary liquid refrigerant which is maintained at a level vwhich provides -a liquid-vapor interface, and that the tubes 212 and interconnected passages 204 constitute Aan enclosed circuit having parts in heat transfer relation to the liquid-vapor interface. Heat received from articles within the compartmentC is absorbed by the secondary refrigerant in the passages 200 with consequent evaporatiolnand the vapors travel upwardly through the headers 210 and then into the tubes 212, at which place the vapors transfer their latent heat to the primary refrigerant, condense and run back into the passages 21141- The embodiment shown in Figs. 9t o 11 is somewhat similar to that shown in Figs, 6 to 8V and comprises a compartment CQ which is defined by a generally rectangular shell or housing 301, theiront and side, edgesrof which carryvhinges 302 for supporting a pair or `:,tccesswdoors. 304. Within they housing 301 is an inner U-shaped plate 305 and an outer U-shaped plate 306 formed with spaced parallel grooves 308 which extend along the bottom Wall and up the side walls. The plate 306 is also formed with a pair o header grooves 309 at the bottom wall and a pair ofI header grooves 310 at the upper part of the sidev wall, the header grooves extending transversely of the parallel grooves 308 and providing in eiect inlet and outlet manifolds interconnecting the passages defined by the grooves 308. Spaced from the rear Wall of the housing 301 is a partition 312 (Fig. 11)' which deiines a cham-- beil :for receiving an evaporator 315 which consists essentially of an elongate enclosure of ir regular shape, the top Wall portions sloping downwardly from the center to each end, the 4side wall portions being generally vertical and the bottom wall portion being zigzag to provide a pair of spaced valleys 311i and, 31'1 at each side of the center of the enclosure, as shown more clearly in Fig. 10. The apex of the top wall portion is formed with a vapor opening 320 connected with a vapor duct 8b and the valleys 315 and 31'1' are connected with ducts 321 and 322 which converge and join a duct 32d which leads to the sludge drum t8. Within the enclosure 315 is a pair o,

condenser coils v325 and 32E of flattenedsteel tubing bent back and forth to provide six tubes,l each centered at the same level with its lower vportion dipping into the primary refrigerant.

The outer surfaces of the tubes are sandblasted: or otherwise formed with capillary rugosities son that under normal operating conditions the exposed surfaces remain wet with a creeping nlmV of refrigerant.

One end or" each tube 325 and 326 is connected; with a vapor inlet tube 320 which passes through; the top wall of the evaporator 315 and is con-K nected with Vthe vapor manifold or header 310,;

and the opposite end of each tube 325 and 326 is` connected to a condensate return or drain 330- which passes through the bottom Wall of the; evaporator and is connected to the condensate manifold or header 323. The grooves or passages 308, headers 309 and 310, ducts 328 and 330, and tubes 325 and 326 provide an enclosed fluid cir-- cuit which contains a secondary iluid or refriger-` ant such as Freon. In operation, vheat absorbedfrom articles within the compartment C eiectsvaporization oi the secondary iiuid which passes through the duct 332 and header 389 .to the` passages 300.

In the embodiments shown in Figs. 41 and 5 each of the purging outletsz and 3.2* is connected at a low point of the condenser because airis, in general, heavier than the aqueous refrigcrant vapor. If, due tocontained antidreeze vapor or `for other reason the refrigerant vapor is the heavier, :then the connection should be at a high point remote from the vapor inlet, as shown in Figs. i3 and 14, whereinthe same reference characters as used in Figs. 1 and 5 are employed to designate the `same or corresponding parts. In any case the condensed refrigerant is drawn from the: condenser through return 3i which is connected at or close to the lowest point ci the condenser.

While I have shown and described different desirable` embodiments of `the invention, it is to be understood thatthis disclosure ls for the purpose of illustration and that various changes and modifications may be made Without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. Refrigerating apparatus comprising a compartment having side and bottom walls formed with intercommunicating passages, inlet and outlet ducts communicatingwth said passages, an enclosed evaporator in said compartment in heat transfer relation toits upper part, said evaporator containing a liquid primary refrigerant spaced from its upper wall so as to provide a liquidvapor interface, anda conduit extending through said evaporator at a level contiguous to said liquid-vapor interface, one end of said conduit being connected with theinlet duct and the other end 0f said conduit being connected with the outlet duct so as to provide a continuous closed circuit, said circuit `containing a` secondary refrigerant adapted to circulate in response to a temperature differential between said liquidvapor interface and the interior of said compartment, thereby transferring heat from the latter to said interface.

2. Refrigerating apparatus comprising a com partment having side and bottom walls formed with intercommunicating passages, an outlet in the upper part of one of the side Walls connected with said passages and an inlet in the bottom wall connected with said passages, an enclosed evaporator in the upper part of said compartment in heat transfer relation to its upper part, said evaporator containing a primary refrigerant spaced from its upper wall so as to provide a liquid-vapor interface, and a conduit extending through said evaporator at a level contiguous to said liquid-vapor interface, one end of said conduit being connected with said inlet and the other end of said conduit being connected with said outlet so as to provide a continuous closed circuit, said circuit containing a secondary refrigerant having a vapor pressure greater than that of said primary refrigerant and adapted to circulate in response to a ternperature differential between said liquidwapor interface and the interior of said compartment, thereby transferring heat from the latter to said interface.

3. Refrigerating apparatus comprising a conipartment of generally rectangular shape and hav ing hollow intercommunicating side and bottom walls, one of the side Walls having an outlet and the bottom wall having an inlet, an enclosed evaporator in the upper part of said compartment in heat transfer relation to its upper part, said evaporator containing a liquid primary refrigerant spaced from its upper wall so as to provide a liquid-vapor interface below said outlet, a conduit extending through said evaporator at a level contiguous to said liquid-vapor interface, one end of said conduit being connected with said inlet and the other end of said conduit being connected with said outlet so as to provide a continuous closed circuit, said circuit containing a secondary refrigerant adapted to circulate in response to a temperature differential between said liquid-vapor interface and the interior of said compartment, thereby transferring heat from the latter to said interface.

Refrigerating apparatus comprising a compartment having side and bottom walls formed with intercornmunicating passages, header elements at the upper part of said side walls communicating with said passages, an enclosed evaporator in said compartment in heat transfer relation to its upper part, said evaporator containing a liquid primary refrigerant spaced from its upper wall so as to provide a liquid-vapor interface, and a plurality of conduits extending through said evaporator at a level contiguous to said liduid-vapor interface, said conduits being connected with said header elements to provide an enclosed circuit, said circuit containing a secondary refrigerant adapted to circulate in response to a temperature differential between said liquid-vapor interface and the interior cf said compartment, thereby transferring heat from the latter to said interface.

5. Refrigerating apparatus comprising a cornpartrnent having side and bottom walls formed with intercommunicating passages, header elements at the upper part of said side walls communicating with said passages, an enclosed evaporator in said compartment and containing a liquid refrigerant spaced from its upper wall so as to provide a liquid-vapor interface, and a plurality of conduits connecting said header elements and extending through said evaporator at a level such that parts extend above and other parts project below said liquid-vapor interface, the outer surfaces of said conduits being formed with capillary rugosities effective to distribute liquid refrigerant over an extended area of their surfaces, said conduits, header elements and passages dening an enclosed circuit containing a iiuid adapted to circulate in response to a temperature differential between said liquid-vapor interface and the interior of said compartment, thereby transferring heat from the latter to said interface.

6. Refrigerating apparatus comprising a storage compartment of generally rectangular shape and having hollow intercommunicating side and bottom walls defining an enclosure, a header extending along the upper part of each side wall and communicating with said enclosure, an enclosed evaporator in the upper part of said compartrnent said evaporator having a vapor outlet at its upper part and containing a primary refrigerant spaced from its upper wall so as to provide a liquid-vapor interface below said outlet, a conduit extending through said evaporator from one header to the other at a level contiguous to said liquid-vapor interface, said cornpartment containing a secondary refrigerant having a vapor pressure greater than that of the primary refrigerant and adapted to flow in response to a temperature differential between said liquid-vapor interface and the interior of said compartment, thereby transferring heat from the latter to said interface.

'7. Refrigerating apparatus comprising a cornevaporator in the upper part of and in heat` transfer relation to said compartment and having a vapor outlet and containing a liquid primary refrigerant at a level which provides a liquid-vapor interface below said outlet, a conduit extending through said evaporator, said conduit having parts vwhich project above and other parts which extend below said liquid-vapor interface, said conduit connecting said header elements, said compartment containing a secondary refrigerant adapted to reflux in response to a temperature diierential between said liquidvapor interface and the interior of said compartment.

8. Refrigerating apparatus comprising a storage compartment of generally rectangular shape and having hollow inter-communicating side and bottom Walls, one ofthe side walls having an outlet and the bottom wall having an inlet, an enclosed evaporator in the upper part of said compartment in heat transfer relation to its upper part, said evaporator containing a primary refrigerant spaced from its upper Wall so as to provide a liquid-vapor interface below said outlet, a conduit extending back and forth through said evaporator at a level contiguous to said liquid-vapor interface, the ends of said conduit being connected with said inlet and outlet so as to provide a continuous closed circuit, said circuit containing a secondary refrigerant having a vapor pressure greater than that of said primary refrigerant and adapted to circulate in response to a temperature differential between said liquid-vapor interface and the interior of said compartment, thereby transferring heat from the latter to said interface.'

9. Referigerating apparatus comprising a compartment having side and bottom Walls formed with intercommunicating passages, an enclosed evaporator in said compartment in heat transfer relation to its upper part, said evaporator containing a liquid primary refrigerant spaced from its upper wall so as to provide a liquid-vapor interface, and a plurality of conduits extending through said evaporator at a level contiguous to said liquid-vapor interface, said conduits being connected with said passages to provide an en# closed secondary circuit, said secondary circuit containing a secondary refrigerant adapted to circulate in response to a temperature differential between said liquid-vapor interface and the wall of said compartment, thereby transferring heat from the latter to said interface.

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